Digital multifunction reprographic systems are well known and have replaced optical reprographic systems as a way to reproduce images. In these conventional digital multifunction reprographic systems, a scanner accepts a document to be copied and converts the document into electronic image(s). These images, usually in the form of pages, are then passed to a central control unit that may re-order or reorganize these pages and then, depending on the request of the user of the device, send the pages or images to a destination. Often this destination is an attached printing unit that makes one or more copies of the original document.
However, these conventional devices perform many other functions besides simple copying. The central control unit is usually equipped with a combination of hardware and software elements that enable it to accept input from other sources. The other sources may include some sort of network interface and/or an interface to a telephone system to enable FAX input.
The network interface is usually configured so that it can accept jobs to be printed from any computer source that is connected to the network. This configuration normally includes elements that can convert input documents formatted in one or more page description languages (PDLs) to the native format of the printing device.
An important inner component of such a conventional multifunction digital device is the image path. This combination of software and hardware elements accepts the electronic images from a multiplicity of sources and performs any operations needed to convert the images to the format desired for the various output paths. The image path is usually one of the more complex and costly components of such digital multifunction devices.
In some conventional systems, the image path has two parallel paths or methods for rendering binary data into a frame buffer memory. In these conventional systems, image data, which has been identified or classified as picture image data, is rendered in raster sequence, while image data, which has been identified or classified as text image data and graphics image data, is rendered from pre-built tile patterns. The binary tile patterns are created using halftone threshold arrays and are copied into the frame buffer memory inside each object or text boundary to create the appropriate text or graphics image in the frame buffer memory.
The conventional systems, which implement the image path having two parallel paths or methods for rendering binary data into a frame buffer memory, create a bitmap in the frame buffer memory consisting of binary tile patterns combined with the halftoned raster data from picture image data and non-halftoned data. However, the conventional two-path implementation produces text and graphics objects with jagged and poorly formed edges due to the halftoning from clustered dot screens. Moreover, after rendering into a binary format, these conventional systems fail to bridge the gaps between the clusters, thereby failing to smooth the edges of text and graphics.
More specifically, jagged edges, and poorly formed shapes occur because the pixel clusters in the halftone screens only paint spots at a particular frequency and angle. Edges and areas in between the clusters are left blank.
Although higher halftone frequencies with a smaller distance in between the clusters make smoother edges, most conventional laser printers do not print well with the higher frequency screens. On the other hand, with respect to many conventional print engines, the shades are more stable, and appear smoother when the frequencies are between one hundred to one hundred fifty lines per inch.
Thus, a low frequency screen provides for smoother shades but jagged edges, while a higher frequency screen provides for smooth edges but less stable shades.
Therefore, it is desirable to implement an image path having two parallel paths or methods for rendering binary data into a frame buffer memory that produces text and graphics objects without jagged or poorly formed edges. Also, it is desirable to implement an image path having two parallel paths or methods for rendering binary data into a frame buffer memory that bridges the gaps between the clusters, thereby smoothing the edges of text and graphics. Furthermore, it is desirable to implement an image path having two parallel paths or methods for rendering binary data into a frame buffer memory that avoids damaging the more complex picture objects when the same halftone patterns are used for both image paths. Finally, it is desirable to implement an edge smoothing process during rendering that improves the shape and appearance of halftoned objects and halftoned text with the lower frequency screens.